Isotopic finger-printing of contemporary and historic changes in copepod trophic position following a shift in in lake trophy

Abstract Copepods play a central role in freshwater food webs. As primary or secondary consumers they utilize varieties of food items ranging from detritus, bacteria to a wide array of phytoplankton and transfer the energy of primary production to higher trophic levels. During the last decades, many lakes, including Lake Constance, have experienced changes in their trophic status, i.e., eutrophication to oligotrophication. Several studies report species-specific responses of copepods to environmental changes highlighting that the response of copepods to environmental changes should only be analyzed on a species level. We propose to estimate the shift in trophic position of copepods following the change in lake trophy of Lake Constance applying three copepod species that differ in important aspects of their life history i.e., in the presence and timing of diapause & diet – Cyclops vicinus (with typical summer diapause), Mesocyclops leuckarti (winter diapause), and Eudiaptomus gracilis (without diapause). The species with either summer or winter diapause experience environmental and dietary changes only during the seasons when they are active since they are on diapause during the rest of the annual
cycle. Lake Constance is highly suited for such an analysis since the lake is regularly monitored with high sampling frequency and archived materials that date back to early 1960s.
This study will use isotopic and amino acid finger-printing of both recent and archived materials to reconstruct individual species response to past food-web structure during periods of significant ecosystem change.

Keywords Stable Isotopes, zooplankton, copepods, trophic structure

Main advisor Elizabeth Yohannes, University of Konstanz

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